Method for manipulating the topography of a film surface

ABSTRACT

A method for selectively altering a thickness of a radiation sensitive polymer layer including providing a substrate including at least one radiation sensitive polymer layer having a first thickness topography; exposing the at least one radiation sensitive polymer layer through a mask having a predetermined radiant energy transmittance distribution to selectively expose predetermined areas of the at least one sensitive polymer layer to predetermined radiant energy dosages; and, developing the at least one radiation sensitive polymer layer to alter the first thickness topography of the at least one radiation sensitive polymer layer to produce a second thickness topography.

FIELD OF THE INVENTION

This invention generally relates to methods for achieving planar layers(films) in an integrated circuit containing semiconductor device andmore particularly to a method manipulating the topography of a radiationsensitive polymer layer including a photosensitive polymer layer such asa photoresist.

BACKGROUND OF THE INVENTION

Surface topography in semiconductor integrated circuit manufacturing isincreasingly important in the manufacture of multi-level semiconductordevices. The degree of planarization of a surface is recognized to beimportant in the patterning of subsequently formed features since theincreasingly small critical dimensions require substantially planarsurface to accurately transfer patterned features within designtolerances through a mask or reticle by passing radiation through themask to a radiation sensitive surface such as a photoresist. Thenon-planarity of the surface is frequently magnified in subsequentmaterial layer formation and photo-patterning processes.

For example, when depositing a polymeric layer of material, including aphotoresist, the polymer is generally blanket deposited reflecting atopography in the deposited layer including protruding features on thesurface such as metal lines or gate electrodes as well as penetratingfeatures such as trench lines openings and Via openings.

Referring to FIG. 1A is shown an example of the effect that penetratingfeatures such as Via openings have on material deposition. For example,Via openings 16A, 16B, 16C, and 16D are shown formed in a dielectriclayer 15 in a portion of the process wafer substrate 17A having arelatively high density of Via opening features. In contrast, Via 16E isshown in a portion of the process wafer substrate 17B, separated inspace from wafer portion 17A as indicated by lines e.g., 12, having arelatively low density of Via opening features. In prior art processesform forming dual damascene features, for example in a Via firstprocess, a Via opening is first created followed by deposition andetchback of a polymeric layer e.g., 18, to a level where the polymerpartially fills the Via opening to protect the Via in a subsequenttrench etching process where an overlying trench opening encompassingone or more Vias is etched to form a dual damascene structure. In theprocess of depositing a layer of material, for example a polymeric layer18 over the Via openings, the relatively higher density of the Viaopening features in portion 17B of the process wafer substrate consumesa relatively larger portion of the deposited polymer, resulting in arelatively thinner polymer layer 18 overlying the Via openings incontrast with portion 17B having relatively fewer Via openings andproducing in a relatively thicker polymer layer 18 over the featureopening e.g., 16E.

Referring to FIG. 1B, subsequently, in an etchback process, the etchback process produces polymer plugs e.g., 18A, 18B, 18C, 18Drespectively filling varying portions of the Vias e.g., 16A, 16B, 16C,16D which may vary in plug height among each other and be significantlydifferent with respect to plug heights e.g., 18E filling Vias e.g., 16Ein relatively less dense areas of the process wafer e.g., 17B. As aresult of the nonuniform plug heights partially filling the Vias, asubsequent etching step to form the trench portion of a dual damascenestructure will result in exposure of an intervening etch stop layerproviding inadequate Via protection in the etching process or theformation of polymeric etching residues forming a Via fence at an upperportion of the plug. In particular, high aspect ratio Vias requireuniform etching profiles including preventing formation of unetchedresidues around the Via openings during anisotropic etching of anoverlying trench structure in a dual damascene formation process. Theformation of Via fences detrimentally affect subsequent processesincluding adhesion/barrier layer deposition and metal filling depositionfrequently resulting in degraded device performance including electricalpathway open circuits. Consequently, time consuming and complicatedadditional etching processes are required to remove the Via fence orotherwise adjust the Via etching profile increasing processing costs andreducing throughput.

There is therefore a need in the semiconductor processing art to developa method to reliably manipulate the topography of radiation sensitivepolymeric containing layers including improving a planarity to improvesubsequent processes including lithographic and etchback processes toachieve improved device reliability and electrical performance whilereducing processing costs.

It is therefore an object of the invention to provide a method toreliably manipulate the topography of radiation sensitive polymericcontaining layers including improving a planarity to improve subsequentprocesses including lithographic and etchback processes to achieveimproved device reliability and electrical performance while reducingprocessing costs in addition to overcoming other shortcomings anddeficiencies in the prior art.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention provides a method for selectively alteringa thickness of a radiation sensitive polymer layer.

According to a first embodiment, the method includes providing asubstrate including at least one radiation sensitive polymer layerhaving a first thickness topography; exposing the at least one radiationsensitive polymer layer through a mask having a predetermined radiantenergy transmittance distribution to selectively expose predeterminedareas of the at least one sensitive polymer layer to predeterminedradiant energy dosages; and, developing the at least one radiationsensitive polymer layer to alter the first thickness topography of theat least one radiation sensitive polymer layer to produce a secondthickness topography.

These and other embodiments, aspects and features of the invention willbecome better understood from a detailed description of the preferredembodiments of the invention which are described in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are representative cross sectional side views of anexemplary dual damascene manufacturing process at stages in themanufacturing process according to the prior art.

FIGS. 2A-2C are representative cross sectional side views of anexemplary implementation of the present invention in a dual damascenemanufacturing process at stages in the manufacturing process accordingto an embodiment of the present invention.

FIG. 3A is a representative data representation of a variation inmaterial removal rate in an exemplary development process versus radiantenergy exposure of a radiation sensitive polymer layer employedaccording to an embodiment of the present invention.

FIG. 3B is a representative cross sectional side views of an exemplaryexposure mask according to an embodiment of the invention.

FIGS. 4A and 4B are representative cross sectional side views of anexemplary implementation of the present invention in a semiconductorfeature manufacturing process at stages in the manufacturing processaccording to an embodiment of the present invention.

FIG. 5 is an exemplary process flow diagram including severalembodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the method of the present invention is explained by exemplaryreference the formation of a Via-first method of formation of a dualdamascene structure in a multi-level semiconductor device, it will beappreciated that the method of the present invention is equallyapplicable to any micro-fabrication manufacturing process where thetopography of a radiation sensitive polymeric layer may beadvantageously manipulated including improving a surface planarity ofthe polymeric layer over a substrate. By the term “radiation sensitivepolymeric layer” is mean any polymeric material that may be altered byradiation including photons and electrons to alter a structure of thepolymeric material and thereby alter a layer thickness changing rate(material removal rate) of the polymeric layer by a layer thicknessaltering process including chemical dissolution, ablation, vaporization,and thermal heating. Although the method of the present invention isparticularly advantageous in the formation of dual damascene structures,for example a copper filled dual damascene structure formed in a lowdielectric constant (low-k) dielectric insulating layer, it will beappreciated that the method of the present invention is equallyapplicable in producing an improved planarity of the radiation sensitivepolymeric layer deposited over protruding substrate surface featuressuch as metal lines and gate electrodes.

In a first embodiment of the present invention a blanket depositedradiation sensitive polymer layer is provided over a substrate. A maskor a reticle including a predetermined density of radiant energytransmitting features is provided to selectively transmit apredetermined radiant energy dosage through the mask to expose selectedportions of the radiation sensitive polymer layer thereby producingdifferential material removal rates over selected thickness portions ofthe radiation sensitive polymer layer in a subsequent developmentprocess. A development process is then carried out to remove selectedthickness portions of the radiation sensitive polymer layer to producean altered thickness topography of the radiation sensitive polymerlayer.

For example, in an exemplary implementation of the present invention,referring to FIGS. 2A-2C, are shown cross sectional side views ofportions of a multi-level semiconductor device at stages in a dualdamascene manufacturing process. Referring to FIG. 2A, a plurality ofVia openings, e.g., 26A, 26B, 26C, 26D are formed in dielectricinsulating layer 24 in process wafer area 27A and juxtaposed alongsideisolated Via 26E formed in another area of the process wafer e.g., 27B,separated in space on the process wafer as indicated by lines e.g., 22.For example, the dielectric insulating layer 24 may be formed of a lowdielectric constant material such as fluorinated silicate glass (FSG) orcarbon doped silicate oxide. It will be appreciated that the dielectricinsulating layer 24 may be formed of two or more dielectric insulatinglayers including etch stop layers (not shown) separating the dielectricinsulating layers. Also shown, an etch stop layer 20A such as siliconnitride (e.g., Si₃N₄) or silicon carbide (e.g., SiC) may be formedunderlying the dielectric insulating layer 24 together with an overlyingetch stop/bottom anti-reflectance coating (BARC) layer 20B such assilicon oxynitride formed overlying the dielectric insulating layer 24.

Still referring to FIG. 2A, a radiation sensitive polymer layer 28 isblanket deposited by a conventional method such as a spin on processover the wafer process surface (substrate). The radiation sensitivepolymer layer 28 is preferably a polymer sensitive to at least oneradiant energy source, for example a photosensitive polymer such as aphotoresist used in lithographic processes such as UV (ultraviolet), DUV(deep UV), EUV (Extreme UV), X-Ray, electron beam exposure methods suchas SCALPEL, and ion projection lithography (IPL). For example, theradiation sensitive polymer layer may be positive or negative acting andpreferably includes at least one matrix polymer and at least onemodifier polymer whereby the radiation sensitive polymer layer uponexposure to a level of radiant energy has a removal rate in adevelopment process, for example made more or less soluble in adeveloper solution.

In one embodiment, the modifier copolymer depolymerizes when exposed toradiation and is vapor developable, for example by a self-development orbaking development method. Preferably, the matrix polymer is selectedsuch that it does not interfere with the modifier polymer when exposedto radiation, for example avoiding cross-linking at the exposurewavelength. In addition, the matrix polymer is advantageously selectedto be compatible with the modifier polymer and provide a sufficientlydifferent removal rates in exposed versus unexposed portions of theradiation sensitive polymer layer in a subsequent development process,for example to obtain an improved surface planarity of the radiationsensitive polymer layer. There are a wide variety of radiation sensitivepolymer materials commonly known in the lithography art including atleast one matrix polymer and at least one modifier or co-polymer, alsoreferred to as resists, which undergo a photochemical change uponexposure to radiant energy thereby altering a material removal rate ormaterial shrinkage rate in a subsequent development process.

Following deposition of the radiation sensitive polymer layer 28, forexample a photoresist, including an optional softbake step below a glasstransition temperature, the topography of the radiation sensitivepolymer layer is measured, for example by interferometry or byprofilometry. A radiation dose necessary to achieve a desired topographyfollowing a subsequent development process is determined, for exampleimproved photoresist layer planarity. Depending on the developmentmethod, for example, chemical dissolution, vaporization,self-development, baking, or ablation, including laser ablation or dryetching, a material removal rate or thickness change rate is preferablydetermined in response to a radiant energy exposure dose delivered overa selected thickness portion of the radiation sensitive polymer layer.For example, in one embodiment, a height difference of a positive actingresist layer is determined with respect to relatively thinner areas ofthe resist layer determine a desired radiation dose to selectivelydeliver to the relatively thicker areas to increase a dissolution rateof a predetermined thickness portion the relatively thicker areas in asubsequent development process for example, to remove predeterminedthickness portions of the resist layer to improve the planarity of theresist layer.

For example, referring to FIG. 3 is shown representative data line 31 ofa radiation sensitive polymer layer (e.g., resist layer) removal rate(thickness change rate) shown on the vertical axis versus radiant energydose (e.g., mJ/cm²) on the horizontal axis. The radiant energy dosewithin the radiation sensitive polymer layer is determined for example,according to an energy integrator measurement and modified according tocalculated or measured constructive and destructive interferenceoccurring within the resist layer caused by reflections from anunderlying material layer interface, for example a BARC layer. Theradiant energy dose and consequent material removal rate as indicated indata line 31, for example a dissolution rate or dry etching rate, ispartially dependent on the thickness of the radiation sensitive polymerlayer. For example, if the resist thickness is within a certainthickness window, the resist removal rate will fall within a linearregion e.g., area A where the resist removal rate in the developmentprocess may be adjusted linearly with an increase or decrease in radiantenergy dosage.

For example, in the case where a chemical development process is used,for example using tetra methyl-ammonium hydroxide (TMAH) or the like,the resist removal rate may be determined by a sequential dip, dry andthickness measurement technique following a given radiant energy dose(exposure). More preferably, in-situ laser interferometry is used todetermine the dissolution rate, for example by monitoring the reflectedlight from the underlying layer, for example a BARC or SiO₂ containinginterface underlying the resist layer. Similar laser interferometrytechniques may be used to measure a resist removal rate or resist layerthickness shrinkage rate for other development methods includingablation, self-development, and baking.

Referring to FIG. 3B, following determination of a desired radiantenergy dosage to achieve a desired topography, for example improvedplanarity of the radiation sensitive polymer layer (resist layer), acontrolled radiant energy exposure mask 33, for exposing selectedportions of the process surface with the desired radiant energy dosageis formed, for example by mapping a desired radiant energy dosage forrelatively thicker portions of the resist layer into a desiredtransmittance for the controlled radiant energy exposure mask 33.Conventional methods are used to form the controlled radiant energyexposure mask to controllably transmit a radiant energy with the desiredradiant energy dosage to selected portions of the photoresist layer. Inone embodiment a proximity alignment correction method using a proximityalignment method is used to add desired mask features to achieve adesired transmittance. For example, the mask typically includes asubstrate of quartz 34 with features such as phase shifting features andattenuating features e.g., 35A, 35B, 35C, 35D formed at a predetermineddensity distribution. For example the mask features may include one ormore of transparent, semitransparent, and opaque features (e.g.,transmittance between about 0 and 1). In a preferred embodiment, themask features include subresolution features, for example including atleast one of lines, holes, islands or any other shaped subresolutionfeature to controllably alter the transmittance of radiant energy. Itwill be appreciated subresolution features operate to scatter light in acontrolled manner to achieve a desired transmittance while avoidingforming a latent image of the subresolution feature in the resist.

Following forming the controlled radiant energy exposure mask totransmit a predetermined radiant energy dosage, an exposure process iscarried out using conventional apparatus and exposure methods. Forexample, the predetermined radiant energy dosage may be selectivelydelivered to selected portions of the radiation sensitive polymer layerthrough the controlled radiant energy exposure mask using conventionalalignment and exposure methods. For example, preferably, a step and scanmethod using one of a mirror projection alignment method, a proximityalignment method, a contact alignment method, and the like. A step andstitch method may be suitably used as well.

Referring back to FIG. 2B, following controlled exposure to apredetermined radiant energy dosage through the controlled radiantenergy exposure mask, the resist layer is developed according to atleast one of ablation, vaporization, self-development, baking, andchemical dissolution methods. For example, the topography of the resistlayer is controllably altered in a predetermined manner in thedevelopment process in response to the selectively introduceddifferential material removal rates by the radiant energy exposureprocess, for example between exposed and unexposed portions of theresist layer produced by the predetermined radiant energy dosagedelivered through the controlled radiant energy exposure mask. Forexample, in a process to improve the planarity of the photoresist layer,portions of the resist layer having a relatively greater thickness, forexample process wafer areas having a relatively lower density of openingfeatures, for example isolated Via opening 26E in process wafer portion27B, are selectively exposed to a relatively higher radiant energydosage to produce a relatively increased dissolution rate in asubsequent developing process thereby selectively removing a relativelygreater amount of resist layer 28 thickness portions to produce a resistlayer with improved planarity. For example, resist layer 28 is producedhaving about the same thickness as the resist layer portion overlyingprocess wafer portion 27A having a relatively lower thickness and ahigher density of features, for example Via openings 26A, 26B, 26C, 26D.

Referring to FIG. 2C, following the selective radiant energy exposureand development process to improve a planarity of the process surface,an etchback process is carried out to etch back the resist layer 28, forexample by a conventional oxygen containing dry etching process to formVias at least partially filled with resist plugs. e.g., 28A, 28B, 28C,28D, and 28E, preferably formed at about the same level, for exampleabout a level equal to the depth of a subsequently formed overlyingtrench. It will be appreciated that the selectively controlled radiantenergy exposure method of the present invention advantageously resultsin a more uniform height of Via plugs over the process wafer surfacefollowing the etchback process thereby improving an etching profile in asubsequent overlying trench etching process while avoiding the formationof Via fences formed of etching resistant residues.

Subsequent conventional processes are then carried out to complete thedual damascene structure including a second photolithographic patterningprocess and etching of overlying trench line openings to overly andencompass one or more Via openings.

In the exemplary embodiment of the present invention shown in FIGS.2A-2C, the more uniform height of the Via plugs e.g., 28A, 28B, 28C,28D, and 28E formed following the selectively controlled radiant energyexposure method etchback process of the present invention provides animproved trench etching process whereby at least a predetermined lowerportion of the Via openings are protected in the trench etching processthereby avoiding the formation of Via fences and improving a dualdamascene opening etching profile. Further, since a resist coater andscanner for exposing the photoresist are in line, the method of thepresent invention is more cost effective in terms of wafer cycle timecompared to an etchback process or CMP process to planarize a resistlayer.

Referring to FIGS. 4A and 4B, a similar process of planarizing aradiation sensitive polymer layer, for example a photoresist layer,overlying a protruding feature is shown. For example, a protrudingfeature 44 such as a gate electrode or etched metal line is shownprotruding from substrate 42. A photoresist layer 46 is blanketdeposited over the feature 44 followed by determining a first thicknesstopography of the photoresist layer 46 and a desired radiant energydosage, for example DUV light, desired to deliver to the photoresistlayer 46 to achieve an improve planarity of photoresist layer 46.Following formation of a controlled radiant energy exposure mask havingthe desired transmittance properties as explained with respect to theembodiment shown in FIGS. 2A through 2C, the photoresist layer 46 isexposed thorough the controlled radiant energy exposure mask anddeveloped, for example by a chemical dissolution method to remove athickness portion of the photoresist layer 46 to improve a surfaceplanarity as shown in FIG. 4B. As a result of the improve planarity ofthe photoresist layer, the resolution and critical dimension oflithographically patterned features in the photoresist layer is improvedthereby avoiding the cumulative effect of defocus in a multi-levelmanufacturing process.

Referring to FIG. 5 is shown a process flow diagram including severalembodiments of the present invention. In process 501, radiationsensitive polymer layer such as a resist is provided. In process 503,the thickness topography of the resist layer is determined. In process505, a desired radiant energy exposure (dosage) of the resist layer isdetermined to produce subsequent thickness following a developmentprocess, for example improve a surface planarity. In process 507, theresist is exposed to radiant energy through an exposure mask tailored tohave the desired radiant energy exposure (dosage). In process 509, theresist is developed to produce the subsequent thickness topography ofthe radiation sensitive polymer layer, for example, to improve a surfaceplanarity. As indicated by directional arrow 511, processes 503 through509 may optionally be repeated.

The preferred embodiments, aspects, and features of the invention havingbeen described, it will be apparent to those skilled in the art thatnumerous variations, modifications, and substitutions may be madewithout departing from the spirit of the invention as disclosed andfurther claimed below.

1. A method for selectively altering a thickness of a radiationsensitive polymer layer comprising the steps of: providing a substratecomprising at least one radiation sensitive polymer layer having a firstthickness topography; exposing the at least one radiation sensitivepolymer layer through a mask having a predetermined radiant energytransmittance distribution to selectively expose predetermined areas ofthe at least one sensitive polymer layer to predetermined radiant energydosages; and, developing the at least one radiation sensitive polymerlayer to alter the first thickness topography of the at least oneradiation sensitive polymer layer to produce a second thicknesstopography.
 2. The method of claim 1, wherein the predetermined radiantenergy transmittance distribution is determined according to the firstthickness topography.
 3. The method of claim 2, wherein the firstthickness topography is determined according to one of profilometry orinterferometry or scanning electron microscope.
 4. The method of claim1, wherein the step of exposing produces a differential material removalrate in the step of developing according to the predetermined radiantenergy transmittance distribution.
 5. The method of claim 4, wherein thestep of developing comprises at least one of ablation, vaporization,self-development, baking, and chemical dissolution.
 6. The method ofclaim 1, wherein the mask comprises subresolution features with apredetermined density distribution.
 7. The method of claim 6, whereinthe subresolution features comprise at least one of lines, holes andislands.
 8. The method of claim 1, wherein the mask comprisessemitransparent areas with a predetermined density distribution.
 9. Themethod of claim 1, wherein the second thickness topography comprises animproved surface planarity compared to the first thickness topography.10. The method of claim 1, wherein the substrate comprises asemiconductor wafer having a process surface comprising at least one ofsurface protruding and surface penetrating features.
 11. The method ofclaim 10, wherein the surface penetrating features comprise at least oneof Vias openings and trench openings.
 12. The method of claim 10,wherein the surface protruding features comprise at least one of gateelectrodes and metal lines.
 13. The method of claim 1, wherein the stepof exposing comprises at least one of alignment, stepping, and scanning.14. The method of claim 1, wherein the step of exposing comprises atleast one of a step and repeat method, a mirror projection alignmentmethod, a proximity alignment method, a contact alignment method, and astep and stitch exposure method.
 15. A method for selectively alteringthe thickness topography of a radiation sensitive polymer layercomprising the steps of: providing a semiconductor wafer having aprocess surface comprising at least one of surface protruding andsurface penetrating features; blanket depositing a radiation sensitivepolymer layer; determining an initial thickness topography of theradiation sensitive polymer layer; determining a desired radiant energydosage to deliver to portions of the radiation sensitive polymer layerto selectively alter predetermined thickness portions of the radiationsensitive polymer layer in a subsequent developing process to produce asubsequent thickness topography of the radiation sensitive polymerlayer; providing an exposure mask for delivering the desired radiantenergy dosage; selectively exposing portions of the radiation sensitivepolymer layer through the exposure mask to deliver the desired radiantenergy dosage; and, developing the radiation sensitive polymer layer toproduce the subsequent thickness topography.
 16. The method of claim 1,wherein the step of exposing produces a differential radiation sensitivepolymer layer thickness change rates in the step of developing accordingto the desired radiant energy dosage.
 17. The method of claim 15,wherein the step of developing comprises at least one of ablation,vaporization, self-development, baking, and chemical dissolution. 18.The method of claim 15, wherein the exposure mask comprisessubresolution features with a predetermined density distribution. 19.The method of claim 15, wherein the exposure mask comprisessemitransparent areas with a predetermined density distribution.
 20. Themethod of claim 15, wherein the subsequent thickness topographycomprises an improved surface planarity compared to the initialthickness topography.
 21. The method of claim 15, wherein the surfacepenetrating features comprise at least one of Via openings and trenchopenings.
 22. The method of claim 21, wherein the initial thicknesstopography is formed by a blanket deposition method including filling ofthe Vias.
 23. The method of claim 22, further comprising an etchbackprocess following formation of the subsequent thickness topographyhaving improved planarity compared to the initial thickness topographyto produce Via plugs at least partially filling the Vias.
 24. The methodof claim 15, wherein the radiation sensitive polymer layer comprises oneof a photosensitive polymer and a photoresist.
 25. The method of claim15, wherein the steps of determining an initial thickness topographythrough the step of developing the radiation sensitive polymer layer arerepeated.